1. Field of the Invention
The present invention relates to screw presses for extracting liquid from fruits or vegetables or the like, and more particularly to a screw press for extracting the remainder of the liquids in such fruits and vegetables after predraining or prepressing.
2. Description of the Prior Art
Screw presses have been widely used for the extraction of liquids from solids or semi-solids in the food industry. A primary application of such presses is in the grape and wine industry. Our co-pending U.S. patent application Ser. No. 69,110 and Ser. No. 69,174, are for a screw press which may be utilized as a predrainer for removing free run juice from destemmed grapes. The disclosed predrainer press will advantageously remove about 80% of the available juice from the grape must. Thus, the must from the predrainer is relatively dry. Prior art screw presses have difficulty in handling very dry materials. Most such screw presses utilize a large forward pitch feed and pressing screw extending for approximately half the length of the press barrel. The remainder of the barrel is open with a closed door disposed at its outer end. Material introduced into the first thread flights of the feed screw are carried forward and build up in the chamber formed by the open section of the press and the closed door. As more and more material accumulates, a cake is built up within this region with the force from the feed screw threads forcing the cake against the end door. Various door designs have been used; however, a restraining force or back pressure must be applied to the door allowing it to open only when the pressure of the cake exceeds such back pressure. Once the cake is built up and material continued to be fed into such presses, the liquids are squeezed out of the cake of material and passed through screens which normally form the walls of the press barrel. These liquids are collected for further processing. The material forced out of the door as it opens is then collected as waste.
Prior art presses have generally used top-hinged doors and have had difficulties in applying the required back pressure once the door has been forced completely open. As improved door structure in a screw press of this type is disclosed in U.S. Pat. No. 4,117,776 to Hunt which uses a flat surface circular door which can open by sliding horizontally on a shaft concentric with the press barrel with back pressure being maintained on the door by means of a coil spring. The door incorporates cutter bars on its inside surface and a mechanical friction clutch for engaging the door with the shaft which is turning with the feed screw. Thus, when the back pressure of the spring is overcome by the force of the cake, the door opens by sliding back, engaging the clutch and rotating to cut away the cake exiting through the door opening. While superior to the hinged doors, the door construction disclosed in this patent has the disadvantage of not being readily adjustable. As will be discussed hereinafter the operator of a press must be able to control the back pressure of the door if various types of fruit and materials are to be completely dewatered.
When a run is completed with the press of the Hunt patent, the barrel and the feed screw must be cleaned. To this end, the feed screw, feed screw drive shaft, and the door are mounted on a carriage such that the feed screw may be completely withdrawn from the barrel for cleaning. This arrangement is relatively complex and expensive.
Most prior art presses are relatively slow to build up the cake in the pressing chamber, and additives such as paper straw and the like are commonly introduced to more quickly build the cake but at added expense and reduction in efficiency of liquid extraction. Our present invention is a screw press especially suitable for predrained or relatively dry materials and which overcomes the above noted problems in the equipment of the prior art.